By 1636, he was captain in an infantry regiment which unsuccessfully defended Stargard against an Imperial force; he narrowly escaped court martial after accusing his commanding officer of negligence.

[3] In May 1636, France formally entered the Thirty Years War in alliance with Sweden; the rapid expansion of the French army created vacancies for experienced officers and de Souches used the opportunity to return home.

Although both actions were unsuccessful, he impressed his superiors sufficiently to be given command of defending Brno in May 1645 against a force led by Lennart Torstensson; after a siege described as "one of the epic stands of the Imperial army", the Swedes retreated in August having lost 8,000 men.

[7] De Souches was rewarded with promotion to the rank of general and granted lands outside Brno; when the war finally ended in 1648, he was placed in charge of supervising the withdrawal of Swedish troops from Moravia and made Governor of Špilberk Castle.

[9] In 1659, he was given command of an army of 13,000 which invaded Swedish Pomerania and besieged Stettin; before the town fell, the Treaty of Oliva ended the war in May 1660, while de Souches quarrelled with his colleague Raimondo Montecuccoli and was ordered home to Moravia.

[11] Having successfully defended Brno and Olomouc, de Souches was promoted Field Marshall in May 1664 and given command of one of three separate forces operating in Hungary, with the other two led by Montecuccoli and Miklós Zrínyi.

Although he won a minor victory at Levice in July 1664, while Montecuccoli stopped the main Ottoman advance at Saint Gotthard in August, Leopold was concerned by the expansionist policies of Louis XIV of France and agreed the Peace of Vasvár a few days later.

[13] When Austria entered the Franco-Dutch War in 1673 as an ally of the Dutch Republic and Spain, he was appointed commander of Imperial troops in the Low Countries and took part in the Battle of Seneffe in August 1674.

The Imperial troops suffered minimal casualties in what was the bloodiest battle of the war and his Allies subsequently claimed de Souches had ignored requests for support.